Hope so U get So much info about Windows process Scheduling :)

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3. ◦ Muhammed Talha MCS-13-08
◦ Aitazaz Ahsan MCS-13-38
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4.  Scheduling
 Scheduling Criteria
 Windows Scheduling
 Priority Schemes
 Thread Priority
 Scheduling Features in Windows
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5.  Maximum CPU utilization ? Multiprogramming.
◦ Several processes are kept in memory at one time.
◦ Any process can take over the CPU.
 Process Scheduler is the component of the OS.
 Scheduling of the CPU is fundamental to OS design.
Ref: William Stalling
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6.  Assign processes to be executed by the processor over time.
 Meets System objectives:
◦ Response time
◦ Throughput
◦ Processor efficiency
Ref: William Stalling
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7.  Scheduling function should:
◦ Share time fairly among processes
◦ Prevent starvation of a process
◦ Use the processor efficiently
◦ Have low overhead
◦ Prioritise processes when necessary
Ref: William Stalling
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8.  CPU scheduling is affected by the following :
◦ (N) A process switches from running to waiting state
◦ (P) A process switches from running to ready state
◦ (P) A process switches from waiting to ready state
◦ (N) A process switches from running to terminate
state
 Circumstances 1 and 4 are non pre-emptive; “they offer
no schedule choice”
 Circumstances 2 and 3 are pre-emptive; “they can be
scheduled”
Ref: William Stalling
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9. Ref: William Stalling
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10.  The dispatcher module gives control of the CPU to the
process selected by the short-term scheduler; this
involves:
◦ switching context
◦ switching to user mode
 The dispatcher needs to run as fast as possible, since it
is invoked during process context switch.
 The time it takes for the dispatcher to stop one process
and start another process is called dispatch latency.
http://en.wikipedia.org/wiki/Scheduling_(computing)
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11.  Different CPU scheduling algorithms have different
properties.
 The choice of a particular algorithm may favour one
class of processes over another.
 In choosing which algorithm to use, the properties of the
various algorithms should be considered.
Ref: William Stalling
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12.  Criteria for comparing CPU scheduling algorithms may
include:
◦ CPU utilization
◦ Throughput
◦ Turnaround time
◦ Response time
◦ Waiting time
Ref: William Stalling
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13.  First Come, First Served (FCFS)
 Shortest Job First (SJF)
 Priority
 Round Robin (RR)
Ref: William Stalling
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14.  DOS-Based
◦ Windows 3.1x
 Windows 9x
◦ Windows 95, 98, ME
 Windows NT
◦ 2000, XP, Vista, 7, 8, 10
 Windows Server
◦ 2003, 2008, 2012
 Windows Mobile
 Windows Phone
◦ 7, 8, 10
http://en.wikipedia.org/wiki/Windows_NT
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15.  MS-DOS is non-multitasking, and as such did not
feature a schedule.
 Windows 3.1x used a non-preemptive scheduler,
meaning that it did not interrupt programs.
 Windows 95 introduced a rudimentary preemptive
scheduler.
http://en.wikipedia.org/wiki/Scheduling_(computing)
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16.  Windows NT-based operating systems use a multilevel
feedback queue. 32 priority levels are defined,
◦ Give preference to short jobs.
◦ Give preference to I/O bound processes.
◦ Quickly establish the nature of a process and schedule
the process accordingly.
All processes receive a priority boost after a wait
event, but processes that have experienced a keyboard
I/O wait get a larger boost than those that have
experienced a disk I/O wait.
http://www.ukessays.com/essays/information-
systems/compare-cpu-scheduling-of-linux-and-
windows.php
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17.  Windows XP schedules threads using a priority-based,
pre-emptive scheduler with a flexible system of priority
levels that includes round-robin scheduling within each
level.
 The scheduler ensures that the highest priority thread
will always run.
 The portion of the Windows kernel that handles
scheduling is called the dispatcher.
http://en.wikipedia.org/wiki/Scheduling_(computing)
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18.  A thread selected to run by the dispatcher will run until it:
◦ Pre-empted by a higher-priority thread,
◦ Terminates,
◦ Time quantum ends,
◦ Calls a blocking system call such as I/O
 If a higher priority real-time thread becomes ready while
a lower-priority thread is running, lower-priority thread
will be pre-empted.
◦ This pre-emption gives a real-time thread preferential
access to the CPU when the thread needs such
access.
http://en.wikipedia.org/wiki/Scheduling_(computing)
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19. http://en.wikipedia.org/wiki/Multilevel_feedback_queue
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20.  The dispatcher uses a 32-level priority scheme to
determine the order of thread execution
 Priorities are divided into two classes
◦ The variable class contains threads having priorities 1
to 15
◦ The real-time class contains threads with priorities
ranging from 16 to 31
◦ There is also a thread running at priority 0 that is used
for memory management
Ref: William Stalling
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21.  The dispatcher uses a queue for each scheduling priority
and traverses the set of queues from highest to lowest
until it finds a thread that is ready to run
 If no ready thread is found, the dispatcher will execute a
special thread called the idle thread
Ref: William Stalling
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22. Ref: William Stalling
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23.  The Windows Win32 API identifies six priority classes to
which a process can belong as shown below
◦ Real-time priority class
◦ High priority class
◦ Above normal priority class
◦ Normal priority class
◦ Below normal priority class
◦ Low priority class
 Priorities in all classes except the real-time priority class
are variable
◦ This means that the priority of a thread in one of these
classes can change
https://prezi.com/2swi3wc7pger/xp-scheduling/
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25.  Within each of the priority classes is a relative priority as
shown below
 The priority of each thread is based on the priority class
it belongs to and its relative priority within that class
https://prezi.com/2swi3wc7pger/xp-scheduling/
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26.  The initial priority of a thread is typically the base priority
of the process that the thread belongs to
 When a thread’s time quantum runs out, that thread is
interrupted
 If the thread is in the variable-priority class, its priority is
lowered
◦ However, the priority is never lowered below the base
priority
 Lowering the thread’s priority tends to limit the CPU
consumption of compute-bound threads
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27.  When a variable-priority thread is released from a wait
operation, the dispatcher boosts the priority
◦ The amount of boost depends on what the thread was
waiting for
 A thread that was waiting for keyboard I/O would get
a large increase
 A thread that was waiting for a disk operation would
get a moderate increase
 This strategy tends to give good response time to
interactive threads that are using the mouse and
windows
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28.  It also enables I/O-bound threads to keep the
I/O devices busy while permitting compute-
bound threads to use spare CPU cycles in the
background
 This strategy is used by several time-sharing
operating systems, including UNIX
 In addition, the window with which the user is
currently interacting receives a priority boost to
enhance its response time
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29.  When a user is running an interactive program, the
system needs to provide especially good performance
for that process
 Therefore, Windows XP has a special scheduling rule for
processes in the normal priority class
 Windows XP distinguishes between the foreground
process that is currently selected on the screen and the
background processes that are not currently selected
https://msdn.microsoft.com/en-
us/library/windows/desktop/ms685100(v=vs.85).aspx
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30.  When a process moves in the foreground,
Windows XP increases the scheduling quantum
by some factor – typically by 3
 This increase gives the foreground process
three times longer to run before a time-sharing
pre-emption occurs
https://msdn.microsoft.com/en-
us/library/windows/desktop/ms685100(v=vs.85).aspx
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31.  Earlier version of Windows provided a feature known as
Fiber.
 Fibers allowed several user-mode threads (fibers) to be
mapped to a single kernel thread.
 Fibers were of limited practical use.
 A fiber was unable to make calls to the windows API
 So Microsoft introduced a UMS.
http://superuser.com/questions/452780/scheduling-
algorithm-used-in-windows-7
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32.  Windows 7 introduced a user-mode scheduling (UMS),
Which allows application to create and manage threads
independently of the kernel.
 Thus , an application can create and scheduled multiple
threads without involving the windows Kernel scheduler.
 Scheduling threads in user mode is much more efficient
than kernel mode.
http://superuser.com/questions/452780/scheduling-
algorithm-used-in-windows-7
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33. CPU cycle-based thread scheduling
 The scheduler was modified to use the cycle counter
register of modern processors to keep track of exactly
how many CPU cycles a thread has executed, rather
than just using an interval-timer interrupt routine
 This new CPU cycle-based thread scheduling gives a
greater fairness and more deterministic app behavior.
http://en.wikipedia.org/wiki/Technical_features_new_to
_Windows_Vista#Kernel_and_core_OS_changes
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34. WinJS Scheduling
 A new scheduler API in Windows 8.1 lets you set
the priority of tasks and manage jobs.
 This helps you write HTML5 apps that use system
resources more efficiently and provide a more
responsive experience to your users.
https://msdn.microsoft.com/en-
us/library/windows/apps/dn751496.aspx
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35.  Pre-emptive scheduler with a flexible system of priority
levels that includes round-robin with multi level priority
queues.
 Dispatcher used a 32-level priority scheme to determine
the order of thread execution.
 The Windows Win32 API identifies six priority classes
 The priority of each thread is based on the priority class
it belongs to and its relative priority within that class.
 When a variable-priority thread is released from a wait
operation, the dispatcher boosts the priority.
 When a user is running an interactive program, the
system needs to provide especially good performance
for that process.
 Windows XP distinguishes between the foreground
process that is currently selected on the screen and the
background processes that are not currently selected.
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36.  If processer are in idle state which type of thread are to
be executed ?
 Why Fibers are reject to serve as UMS ?
 When dispatcher boost the priority which type of thread
get a large increase ?
 For Which Processes are scheduling quantum by some
factor are increased by (eg75%) ?
 what is the latest Process Scheduling feature used in
windows 8.1 ? And how it’ll beneficial for programmers ?
 How many level priority scheme are used to determine ?
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37. Lottery Scheduling
 Processes are each assigned some number of lottery
tickets.
 Scheduler draws a random ticket to select the next
process.
 The distribution of tickets need not be uniform.
 Granting a process more tickets provides it a relative
higher chance of selection.
 Lottery scheduling solves the problem of Starvation.
Giving each process at least one lottery ticket
guarantees that it has non-zero probability of being
selected at each scheduling operation.
http://en.wikipedia.org/wiki/Lottery_scheduling
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38. http://www.allaboutpresentations.com/
2009/05/what-is-ideal-font-size-for.html
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